1. Field of the Invention
This invention relates to hypodermic syringes for dispensing liquid drugs. More specifically, the present invention pertains to a syringe of the type having a prefilled containment chamber for long term storage of a drug in a known quantity in a sealed condition, and which is readily adapted for emergency dispensing of such stored liquid drug.
2. Prior Art
Numerous prior art emergency syringes are known. However, all such prior art emergency syringes known to the applicant suffer from a number of disadvantages which detrimentally affect their reliability and/or substantially increase their cost of manufacture. In addition, many such emergency syringes of the prior art function in a manner which is inherently dangerous to the patient by allowing the introduction of undesirable particulate matter into the drug as it is being dispensed or by allowing the introduction of a substantial amount of air into the patient along with the drug. In addition, many such prior art emergency syringes require the breaking of a seal or diaphragm which is uded to contain the drug in a non-contaminated condition in a storage chamber. Breaking or piercing such diaphragms requires a certain amount of force that varies significantly from syringe to syringe, rendering such prior art devices generally inconsistent and unpredictable in the degree of difficulty incurred to effect a configuration which permits dispensing of the drug into the patient.
By way of example, such prior art emergency syringes that utilize a diaphragm that is either burst or pierced immediately prior to, or concurrently with, the dispensing of the contained drug into the patient, are disclosed in many of the following patents.
______________________________________ U.S. Pat. No. U.S. Pat. No. ______________________________________ 2,362,165 3,391,695 2,538,390 3,413,974 2,538,391 3,424,155 2,646,798 3,710,794 2,735,429 3,739,779 2,778,360 3,757,779 2,841,144 3,757,780 3,091,240 3,768,473 3,308,821 3,803,700 3,380,449 3,859,999 3,387,609 3,885,297 3,960,139 ______________________________________
The devices disclosed in these patents are generally disadvantageous because the bursting or piercing of a diaphragm or similar structure tends to produce particulate matter that is carried by the drug into the patient and may thereby detrimentally affect the patient. In addition, the force needed to either pierce or burst a diaphragm or the like is generally not consistent from syringe to syringe because of the inherent difficulty in providing a diaphragm of precise dimensions. They must be sufficiently thick to provide adequate sealing and still be sufficiently thin to yield to a reasonable amount of piercing force. There is an additional problem incurred when emergency syringes utilizing diaphragms and the like contain drugs that are chemically active to result in increased pressure within the sealed containment chamber. By way of example, syringes of the type herein disclosed are desirable for emergency treatment of cardiac victims or the like wherein the drug contained in such syringes is sodium bicarbonate or the like. However, as is well known, most of such drugs are chemically active to the extent that some form of gaseous vapor such as carbon dioxide gas is given off, particularly at elevated temperatures. Accordingly, at higher temperatures, enough carbon dioxide gas may be produced to result in a pressure level within the containment chamber sufficient to prematurely burst or break the diaphragm and release the drug from the containment chamber, contaminating the drug and rendering the syringe useless.
Although one additional prior art emergency syringe known to the applicant does not fall within the above-indicated category of prior art syringes, it also suffers from a number of highly disadvantageous characteristics which render it far less desirable than the invention disclosed and claimed herein. More particularly, the device disclosed in U.S. Pat. No. 3,967,759 to Baldwin et al discloses a syringe that utilizes a pop-out valve plug seal in the nose end of a glass tube with a plunger piston at the opposite end.
Although the device disclosed by Baldwin et al (U.S. Pat. No. 3,967,759) is perhaps more relevant to the applicant's invention in that it does not require the use of a burstable or pierceable diaphragm, it still suffers from a number of disadvantages relating to the inconsistent amount of force required to unseal the containment chamber, the high cost of manufacture, and the potentially dangerous, unacceptably large volume of air that is introduced with the liquid drug dispensed into the patient, with or without an attempted purging of the air prior to injection. In addition, its structure still renders it susceptable to premature escape of the liquid drug within the containment chamber in applications involving sodium bicarbonate solution and similar drugs in which there is a substantial increase in internal vapor pressure, particularly at elevated temperatures. In addition, very precise manufacturing tolerances for an unusual glass tube geometry disclosed in the above-indicated Baldwin et al patent, increases the cost of manufacture. Further, during the drug dispensing (injection) process, the loosened rubber stopper may unexpectedly plug the fluid path and stop the dispensing which can be dangerous or even fatal to the patient.